1. Field of the Invention
The present invention relates generally to cranes, and more particularly to a system which extends the effective height of a crane, and even more particularly to a system which can be used in the conducting of RF drive tests.
2. Description of Related Art
With the proliferation of radio frequency transmissions, particularly in conjunction with the ever increasing use of cellular telephones, optimization of the geographical placement of cellular towers with their attendant antennas has become very important. To confirm the correctness of the location of the tower, before the tower is actually erected in place, a testing of the proposed location is conducted due to the costs involved in the tower's erection and the potential misallocated costs involved if the geographical placement is either unacceptable or demonstrably less than desirable.
This testing commonly takes the form of a RF drive test, also referred to as just a drive test, wherein a signal from the location of the proposed tower is emitted and then received on the ground by equipment in a vehicle, with the vehicle being driven around the vicinity of the proposed tower location in order to pinpoint where the transmitted signal can actually be picked up.
The situation is made more complicated by the fact that there are two type of antennas. The first type of antenna used in this type of transmission system is an omni antenna. The signal emitted by this type of antenna goes out relatively uniformly in all directions, similar to the waveform created when a pebble is tossed into a pond. The second type of antenna used in this type of transmission system is a directional antenna. With a directional antenna, a frequency can be emitted in a certain direction. This type of antenna is sometimes desirable because buildings, trees, or even the terrain can affect the ability to receive a signal.
For example, because of congestion, police radios or whatever may want to make use of directional antennas to transmit from tower to tower to tower with the ultimate goal being that the signal can be received and effectively transmitted from an omni antenna. By way of another example, if the proposed tower location is on top of a big hill with the desired coverage area being around the hill, then an omni antenna is fine. However, if you have a building adjacent the proposed tower location, then you are not going to benefit from using an omni directional antenna. In fact, it is more desirable to transmit away from the building and avoid interference. In such cases a directional antenna is preferred. Directional antennas are also used where the tower takes the form of a water tower, such that a plurality of antennas are spaced on the curved side of the water tower. When a proposed site destined for a directional antenna is tested, the test is conducted with a directional antenna, not an omni.
Crane systems have been used to simulate the existence of a tower, thereby permitting a drive test to be conducted without going to the time and expense of erecting a permanent tower. These systems use a 10' wide truck that in total weighs 140,000 pounds. While the truck and crane itself only weighs 60,000-80,000 pounds, by the time the counter weights, mounting basket, and additional test equipment are added, it weighs up to 140,000 pounds. Typically, another semi with nothing but the counter weights and rigging is used.
Drive tests often need to be conducted at heights of between 150 and 200 feet, which to date has required the use of trucks which need permits due to the size of trucks used in conjunction with the necessary cranes, which in the prior art have normally been of the lattice type. Trucks which need permits can only be moved between the hours 7:00 a.m. and 6:00 p.m. or during daylight hours. Additionally, they are not allowed to run on Sundays. Plus, it usually takes 24 hours to get a permit.
Because the size of the truck used in the prior art is 10' wide, it requires a runner truck, and needs to be labeled "WIDE LOAD" with the accompanying flags. With a truck that big there can be problems. Just getting back to where the test is to be run, one wrong turn and what was a 8' drive becomes a 15' wide path. Additionally, extra space is needed once the crane truck is in position: extensions have to be put out so that the truck doesn't tip over. Thus with the prior art, each of the outriggers add another 10-15' to the width of the entire project.
Additionally, the typical prior art crane system has its drawbacks. For example, there can be interference from an omni antenna because of the existence of the crane on one of the sides. The advantage of the relatively smaller trucks is that they do not require permits, nor take up as much space, however, they heretofore have been unable to reach the heights necessary to conduct drive tests. Plus, typically two trucks are needed, due to the counter weights, and the size and weight of the boom sections. Also, the fact that only a certain height can be reached with the 38, 30 and 23.5 ton extendable boom cranes, if greater heights than 150' are required, then a bigger boom or bigger crane, such as a lattice type crane, is needed which translates, as has been discussed above, into more set up area, more set up time, the obtaining of permits, more cost, and at least two men to do it. For example, in order to conduct a drive test at the 200' level, the crane must be heavier than a 30 ton unit.
It is thus apparent that the need exists for a device or system that can extend the effective height of a crane which overcomes the problems associated with the prior art. Such a or system should be capable of being used with various brands of cranes.